ext_conf_builder.rb: use RUBYOPT

* lib/rubygems/ext/ext_conf_builder.rb (Gem::Ext::ExtConfBuilder.build):
  use RUBYOPT instead of -r option, and revert some tests.  [Bug #7698]


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@39559 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
ext_conf_builder.rb: hack for obsolete sytle gems

* lib/rubygems/ext/ext_conf_builder.rb
  (Gem::Ext::ExtConfBuilder.hack_for_obsolete_sytle_gems): remove
  circular dependencies for old style gems which locate extconf.rb on
  the toplevel.  [ruby-core:53059] [ruby-trunk - Bug #7698]


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@39560 b2dd03c8-39d4-4d8f-98ff-823fe69b080e